Error opening pdf from email

Respondents are getting an error message “Adobe Acrobat Reader could not open ‘certificate.pdf’ because it is either not a supported file type or because the file has been damaged (for example, it was sent as an email attachment and wasn’t correctly decoded).”

A custom script was used to deliver a certificate upon completion. My investigation of Acrobat shows that the 10.1.5 and 11.0.01 updates improve security by enforcing stricter parsing of the PDF-header. The product now refuses to open the small fraction of PDFs that do not correctly start with the ‘%PDF-‘ header and the error appears.